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Need help for encryption using AN821 for pic16f877

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ganavel9783

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microchip project an821

Hi guys,

I'm currently working on a project to do encryption of text files using PIC16877. There is an Application Note from Microchip.com to do encryption using AN821 (Advanced Encryption Standard using PIC16XXX). I have a serial circuit that i would like to use to send a text file from a PC to be encrypted by PIC16f877.Attached is the serial circuit i'm using to test the code.

The problem i'm facing now are---->>
1) how do i test the code whether it can encrypt a text file or not?
2) how do i send the key for the text to be encrypted?
2) should i send a text file using Hyperterminal to test the code??
3) is there any subroutines i need to add to the assembly source code given so that it can work to take data(text file) serially from PC??
4) what are the changes i should make to make the assembly code work in PIC16f877 since it given for PIC16c22a?

Here is a sample from the source code given by microchip from the following website:
h**p://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en012009

I pasted the main rountines only below here.I didn't include the subrountines for the 4 data tranformation using AES algorithm.Any help will be deeply appreciated.

*** Program: aes_rijn.asm ***
*** This routine takes 16 bytes of data and ***
*** first encrypts it then decrypts it using ***
*** the AES/Rijndael algorithm. ***



list P=PIC16C622A
#include p16c622A.inc
#include TABLES.inc ; Holds S_TABLE & Si_TABLE Data
; Starts at Location 0x0600

__CONFIG _CP_OFF & _WDT_ON & _BODEN_OFF & _PWRTE_ON & _RC_OSC

;****************** Constants ************************
INIT_RAM0 equ 0x20 ; Starting point of RAM in segment 0
ROUNDS equ 0x0A ; number of rounds necessary to cipher/decipher

;****************** Variables ************************
block equ 0x20 ; block vector ( 16 bytes*8 => 128 bits)
key equ 0x30 ; key vector ( 16 bytes*8 => 128 bits)

aux equ 0x40 ; general purpose var
aux1 equ 0x41 ;
aux2 equ 0x42
aux3 equ 0x43

round_counter equ 0x44 ; encryption/decryption rounds counter
rcon equ 0x45 ;

d0 equ 0x4A
d1 equ 0x4B
d2 equ 0x4C

ORG 0x0000
start:
goto main ;

ORG 0x0004

int_handler:

; ***************** END Interrupt Handler ***********************

ORG 0x0010

;********************** MAIN Routine ****************************
; This routine cipher and decipher a given text.
; The init_decryption_key routine was put here to show how to
; create a decryption key from the initial key
;
main:
call init_cpu ; start CPU registers
call set_test_block ; loads the plain text to be ciphered
call set_test_key ; load the key used to cipher
call encrypt ; cipher the code
call set_test_key ; load a second time the key used to cipher
call init_decryption_key ; create the initial decryption key
call decrypt ; decipher the block back to plain text
goto $

; ***************** INIT_CPU ************************************
; This procedure cleans the RAM in segment 0
; Input: None
; Output: None
; ***************************************************************
init_cpu:
movlw INIT_RAM0 ;points to the start of the RAM
movwf FSR
loop_cram0
clrf INDF ;clear RAM location pointed by FSR
incf FSR,f ;increment pointer
btfss FSR,7 ;while FSR < 0x80 loop
goto loop_cram0 ;
return


; ********************* SET_TEST_BLOCK **************************
; This procedure sets the test plain text to be ciphered
; Input:
; Outup: block[16]={B0,B1,...}
; Globals: block,aux,FSR
; OBS: Generates block vector for test;
; ***************************************************************
set_test_block:
movlw 0x0
movwf block+0x0
movlw 0x0
movwf block+0x1
movlw 0x0
movwf block+0x2
movlw 0x0
movwf block+0x3
movlw 0x0
movwf block+0x4
movlw 0x0
movwf block+0x5
movlw 0x0
movwf block+0x6
movlw 0x0
movwf block+0x7
movlw 0x0
movwf block+0x8
movlw 0x0
movwf block+0x9
movlw 0x0
movwf block+0xA
movlw 0x0
movwf block+0xB
movlw 0x0
movwf block+0xC
movlw 0x0
movwf block+0xD
movlw 0x0
movwf block+0xE
movlw 0x0
movwf block+0xF
return
; ********************* SET_TEST_KEY **************************
; This procedure sets the key used to cipher
; Input: None
; Outup: key[16]
; Globals: key[16],FSR,aux
; ***************************************************************
set_test_key:
movlw 0x0
movwf key+0x0
movlw 0x0
movwf key+0x1
movlw 0x0
movwf key+0x2
movlw 0x0
movwf key+0x3
movlw 0x0
movwf key+0x4
movlw 0x0
movwf key+0x5
movlw 0x0
movwf key+0x6
movlw 0x0
movwf key+0x7
movlw 0x0
movwf key+0x8
movlw 0x0
movwf key+0x9
movlw 0x0
movwf key+0xA
movlw 0x0
movwf key+0xB
movlw 0x0
movwf key+0xC
movlw 0x0
movwf key+0xD
movlw 0x0
movwf key+0xE
movlw 0x80
movwf key+0xF
return

---------------------------------------------------------------------
---->>>Subroutines for SubBytes, ShiftRows, MixColumns, AddRoundKey
---------------------------------------------------------------------


; ************************** DECRYPT ******************************
; This procedure decipher the plain text in block using key
; Inputs: The encrypted text in block[],
; The decipher_key in key[]; this key is NOT the
; original cipher key used to cipher the plain text,
; but the scheduled original.
; Outups: The plain text in block
; The original cipher key in key[]
; OBS: This implementation follows as possible the original
; structure and function names used by the reference
; implementation of AES
; *****************************************************************
decrypt:
movlw 0x36
movwf rcon ; RCON initialization
call key_addition ; initial key addition
movlw ROUNDS
movwf round_counter ;
goto dec_first_round
loop_decrypt:
call inv_mix_column
dec_first_round:
call substitution_Si ;
call dec_shift_row
call dec_key_schedule
call key_addition ;
decfsz round_counter,f
goto loop_decrypt
return

; ************************** ENCRYPT ******************************
; This procedure cipher the plain text in block using key
; Inputs: The plain_text in block[]
; The cipher_key in key[]
; Outups: The ciphered text in block
; The rounded (decipher) key in key[]
; OBS: This implementation follows as possible the original
; structure and function names used by the reference
; implementation of AES
; *****************************************************************
encrypt:
movlw 0x01
movwf rcon ; RCON initialization
call key_addition ; initial key addition
movlw ROUNDS ; start the round counter for the loop
movwf round_counter
loop_encrypt:
call substitution_S ;
call enc_shift_row
decf round_counter,w
btfsc STATUS,Z
goto last_round
call mix_column
last_round:
call enc_key_schedule
call key_addition ; key addition
decfsz round_counter,f
goto loop_encrypt
return

; ***************** INIT_DECRYPTION_KEY ***************************
; This procedure creates the initial deciphering key from the initial
; cyphering key by multiple application of enc_key_schedule
; Inputs: The plain_text in block[]
; The cipher_key in key[]
; Outups: The ciphered text in block
; The rounded (decipher) key in key[]
; OBS: This implementation follows as possible the original
; structure and function names used by the reference
; implementation of AES
; *****************************************************************

init_decryption_key:
movlw 0x01
movwf rcon
movlw 0xA
movwf round_counter
loop_init_decryption_key:
call enc_key_schedule
decfsz round_counter,f
goto loop_init_decryption_key
return

;0E DD 33 D3 C6 21 E5 46 45 5B D8 BA 14 18 BE C8

END
 

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